Pre-cast concrete beam construction



Q Id! 4% 7 3 Sheets-Sheet 2 V l-Llll J. B. HENRY ErAL' FEE-CAST CONCRETEBEA" CQNSTRUCTIQN' I I h gjj/a Oct. 18, 1960 Filed Aug. 6, 1957 (Win 32'!1:

Oct. 18, 1960 J. B. HENRY ETAL PRE-CAST CONCRETE BEAM cons'mucnou 3Sheets-Sheet 3 Filed Aug. 6, 1957 QQN '5" mm L w United States PatentPRE-CAST CONCRETE BEAM CONSTRUCTION John B. Henry and Gayle B. Price,Dayton, Ohio, assignors to The Flexicore Co., Inc., a corporation of NewThis invention relates to a pre-cast concrete beam construction and aimsto provide pre-cast concrete beams which may be combined in aconstruction having a smaller deflection for a given load than is trueof simple spans.

In general this invention contemplates the use of reinforced pre-castconcrete beams, the beams having adjacent end portions joined togetherat predetermined portions of the structure to provide continuous beams.The joined ends of the beams are located so that the load transfer fromone beam to another occurs at a region of low or zero moment.

An advantage resulting from the use of the invention resides in thesaving of steel and the use of relatively short beams to provide aconcrete construction which has less deflection or sag between spansthan would be true with the use of simple spans extending between fixedsupports.

A significant feature of the present invention resides in the manner andmeans by which load transfer is effected from one beam end to anadjacent beam end. As is well known, a concrete beam, like any otherbeam, when loaded has a neutral plane separating regions of compressionand tension respectively. Since concrete has poor tensioncharacteristics, a principal objective of steel reinforcement in apre-cast beam is to so locate the neutral plane as to put most of theconcrete in the beam in compression under beam load.

In eflfecting a load transfer from one beam end to another beam end, itis important to insure continuity of load between those portions of thebeam ends which are in compression. As examples, the simple use of dowelbars or pins across the ends while perfectly satisfactory for steel andwood is totally unsatisfactory for pre-cast concrete. This is due to thefact that the load transfer results in tension upon the concrete andconsequent failure.

In accordance with the present invention, means are provided for joiningthe various beams forming part of an entire structure in such a mannerthan an efficient and complete transfer of load from one beam to anotheris effected. In order that the invention may beunderstood, variousembodiments will be disclosed, it being understood that theseembodiments are examples to illustrate the invention and that variationsmay be made without departing from the scope of the invention as definedby the appended claims.

Referring now to the drawings, Figure 1 is a plan view of a portion of aconcrete floor or roof embodying the present invention.

Figure 2 is a section upon line 22 of Figure 1.

Figure 3 is a section along line 33 of Figure 1.

Figure 4 is a top plan view of a portion of a structure using a modifiedform of the invention.

Figure 5 is a section along broken line 55 of Figure 6.

Figure 6 is a section along broken line H of Figure 4,

Figure 7 is a plan view of still another modified form of the invention.

Figure 8 is a section along broken line 8-8 of Figure 9.

Figure 9 is a section along broken line 99 of Figure 7.

Figure 10 is a diagrammatic plan View of slabs arranged to form asuitable floor construction in accord ance with the present invention.

Figure 11 shows some curves illustrating the relative behavior of asimple reinforced concrete slab and a continuous slab constructionembodying the present invention.

While various forms of concrete beams or slabs may be utilized inpracticing the invention, it is preferred to use the cored reinforcedconcrete slabs disclosed and claimed in United States Patent No.2,299,070 and the invention may be disclosed in connection with suchreinforced beams.

Referring for example to Figure 2, there are illustrated in section oneconcrete beam or slab 10 and parts of adjoining slabs 11 and 12.Inasmuch as the slabs are similar in construction, it is only necessaryto describe slab 10 in detail. Slab 10 is of concrete and haslongitudinal steel reinforcement at the four corners, these beingindicated by numerals 14, 15, 16 and 17. In addition, steelreinforcements 18 and 19 are provided, these being approximately in thecenter of the lower part of slab 10.

Slab 10 has longitudinal bores or channels 21 and 22. As is more fullydisclosed in the above identified patent, it is preferred to have thetotal area of cored portions 21 and 22 bear a certain relation to thetotal area of the section of the slab. This area relationship is betweenabout 40% and about 50%. For the purpose of the present inventionhowever, this range of ratios may be varied within limits.

Longitudinal reinforcements 14 to 19 inclusive may consist of steelwhich is tensioned, the slab and reinforcement being so designed thatthe neutral plane is at or near the bottom face of the slab. The slabsare adapted to be disposed in side by side relation and in order to lockadjacent slabs together, grout keys 25 and 26 are provided along the topside portions of each slab for the full length thereof. As isillustrated in Figure 2, when slabs 10, 11 and 12 are disposed in sideby side relation, channels are provided by the grout keys for holdinggrout. The grout keys and the grout thus provide a suitable means forlocking the slabs along the lengths thereof.

As is well known in continuous constructions, beams are disposed in sideby side relation with the ends stag gered so that the end of one beam isrigidly attached to an intermediate portion of an adjacent beam and theload transferred from the supported beam at that point to the suspendedbeam. In concrete slabs, it is necessary to effect this load transferfrom one beam to the other without putting the concrete in tension.

As illustrated in Figure l, beam 14 is a supported slab and beam 10A isa suspended slab. Laterally dis-' posed of beams 10 and 10A are beams 11and 12 which, at the regions illustrated in the drawing, may beconsidered as supported slabs. By supported slabs is meant that theslabs have at least two spaced points along the length thereof at whichthe slab is supported on piers or the like with the end extendingcantilever style beyond a supporting region. The objective of this is totransfer the load from the end of beam 10 to an adjoining end of beam10A. In order to effect this, the opposed beam faces 31 and 32 of thetwo beams are disposed inproximity to each other and have suitable meansto join the beam ends.

Top faces 33 and 33A of the two beams have steel bridge plate 30extending across the gap between faces 31 and 32. Bridge plate 30extends over an extensive portion of the transverse dimension or widthof beams and 10A. The extent of overlap of bridge plate 30 beyond endfaces 31 and 32 of the beams may vary within wide limits but it ispreferred that bridge plate 30' extends for a distance of several inchesbeyond the free ends of the beams.

End 31 of the suspended slab, in this case 10A, has steel stirrup 34rigidly atttached to steel reinforcing rods 14 and 17. As is indicatedin Figure 2, stirrup 34 is of rod or wire and has its ends hooked aroundand welded or rigidly attached to corner reinforcing rods 14 and 17.Stirrup 34 extends upwardly from the lower corners along the side of thebeam within the concrete and across the top of face 33A of the beamoutside of the concrete. It will be noted from Figure 3, that stirrup 34extends enough above top face 33A of beam 10A to provide a clearanceregion into which bridge plate 30 may project.

It is clear that the end of supported beam 10 does not require anystirrup although this may be provided if necessary. Since beam 10 issupported, there will be a tendency to rock bridge plate 30 upwardly insuch a way as to tend to pull stirrup 34 up from beam 10A. A broad areaof bridge plate 30 engages the top surface of face 33A of beam 10A andthe concrete in beam 10A under plate 30 will be compressed by plate 30.The only part of beam 10A which will be in tension will be stirrup 34and this will be sufliciently heavy to withstand the loading.

In addition to the above construction, it has been found that grout keys25 and 26, locking beams 10 and 10A on the one hand to side beams 11 and12, also tends to impart load transfer characteristics. Bridge plate 30should be wide enough-this is the dimension along the length of thebeamso that the bridge plate has a large area upon the top face of eachend portion of beams 10 and 10A. The concrete will therefore not besubjected to excessive compression.

It is preferred to design the entire structure so that the regions ofsupport for supported slab 10 are so selected along the length of theslab that substantially at the end faces of the beams 10 and 10A themoments will be substantially zero. This may be obtained by properlyproportioning the ratio of the portion of the beam extending betweenfixed supports as piers to the cantilever portion in the supported endof the beam.

As an example, beams having a length of thirty-two feet and sixteen feetrespectively may provide a continuous floor supported on piers withtwenty-four foot spans. A thirty-two foot beam would be supported atpoints spaced twenty-four feet apart to leave four feet of cantileverlengths at each end. The sixteen foot beam would be located at a fourfoot cantilever end so that a sixteen foot beam would be suspended andwould not in itself have any pier support.

Referring now to Figure 10, there is illustrated a view of a floor orroof constructionembodying the principles of the invention. Piers, wallsor other rigid supports have their center lines at 40 to 48 inclusive.Except for end piers 40 and 48, the spans are twenty-four feet betweencenters. For convenience in using beam lengths, the end spans are twentyfeet each. Except for end beams or slabs, slabs alternating in lengthsixteen and thirty-two feet are used. It will be clear that forintermediate piers, the junction lines between abutting slab ends arefour feet beyond the pier center lines. It is only certain of the endspans which have to be twenty-four feet long. The slab lengths in feetare shown in the figure.

The above construction uses less steel than one using simple twenty-fourfoot spans throughout, except for the end twenty foot spans. As anexample, a construction as illustrated in Figure 1 will require fivepounds of steel per square foot of floor area for a load of 122 poundsper square foot.

The comparable simple span construction (all slabs are supported) willrequire 6.65 pounds of steel per square foot for the same loading. Inthe above comparison, the extra steel required at slab ends for thecontinuous construction (the bridge plates and steel loops) aredisregarded.

A further advantage of the continuous construction is the greatlyreduced deflection or sag as compared to simple slab construction Wherethe slabs are all supported. The continuous construction in this examplehas about 40% of the sag or deflection of the corresponding simple slabconstruction.

In the above example of continuous construction, the thirty-two footslabs had prestressed steel in both top and bottom parts of a slab. Thesixteen foot suspended slabs had the prestressed steel only in thebottom of the slab, the steel in the top layer being unstressed in thefree slab.

Referring now to Figures 4, 5 and 6, a modified construction isillustrated wherein stirrup 40 is rigidly attached to angle irons 41having portions 42 and 43. Portion 42 of the angle iron is disposed atthe end face of the suspended slab and when the slab is cored as shown,it may be necessary or desirable to shape the angle iron portion toconform to the curvature of the concrete. Portion 43 of the angle ironextends over the top face 45 of the supported slab.

Referring to Figures 7 to 9 inclusive, a still further modification isillustrated wherein'stirrups 47 are rigidly attached to the bottomreinforcing rods as in the previous modifications. Stirrup 47 howeverhas end portion 48 which extends over the top surface 49 of thesupported slab. End portions 48 of the stirrups may be provided withmetal plates below them for distributing the compression force over thetop surface 49 of the slab. V In the practical application of theinvention, the sup ported slab ends will be suitably anchored to thesteel, masonry or other support structure. In the case of steel beams orsupports for the slab ends, the end of the concrete slab may overlie asteel web or tie plate and the steel slab reinforcement may be welded tothe steel web or tie plate.

It is understood that the slab end constructions illustrated in thevarious figures may be applied to one or both ends of a slab.

Referring now to Figure 11, some curves illustrating the behavior undertest of a simple slab and a continuous slab construction embodying thepresent invention are shown. The slabs under test are Flexicore slabsgenerally available on the market and made in accordance with thedisclosure of United States Patent No. 2,299,070 insofar as the corepassages are concerned. I

Both the simple and continuous slabs were tested under increasing loads.The various points on the curve where significant changes occured underload are marked in the figure. Important test points as defined by theA.C.I (American Concrete Institute) are marked. In the figure, L and tmust be measuredin the same units and refer respectively to the lengthof the span and thickness of the slab. A refers to the area of steel.The failure of the beam under diagonal tensioning (abbreviated to DT) isclearly shown as the loading on the beam increases. The curvesillustrate the greater efficiency in the use of steel in a continuousslab construction embodying the present invention.

A continuous slab construction embodying the present invention has farless deflection (sag) than a simple span using the same amount of steeland thus would meet engineering specifications under conditions of costand deflection where a simple span might fail;

In addition to the abovetest curves, a greater safety factor isintrodced in a slab ernbodying the present invention by virtue of thegrout keys along the slab sides. It has been found that the groutconnections between adjacent slab sides tend to distribute the loadbetween supported and suspended slabs to an even greater degree thanindicated by the above curves.

What is claimed is:

1. A pre-cast concrete slab construction comprising parallel, laterallyspaced rigid supports providing supporting regions lying in a generallyhorizontal plane, a plurality of pre-cast reinforced concrete slabssupported by said rigid supports, each slab having a length great incomparison to the width or thickness thereof, the slabs being disposedin the finished construction so that all have their lengths transverselyacross said rigid supports, certain of said slabs being supporting slabsand each having a length greater than the distance between adjacentrigid supports, each supporting slab being disposed to overhe adjacentrigid supports and the end portions thereof extending in cantileverfashion beyond the rigid supports, other slabs being suspended slabs andeach having a length too short to reach between adjacent rigid supports,said supporting and suspended slabs being arranged in a pattern toprovide a continuous slab construction wherein a suspended slab liesbetween the ends of longitudinally aligned supporting slabs and betweenthe sides of laterally spaced adjacent supporting slabs, all suspendedslabs lying between rigid supporting regions and deriving the entiresupport from the ends and sides of adjacent supporting slabs, every slabhaving a generally rectangular cross-section and having flat ends andhaving the sides thereof adjacent the top face shaped so that adjacentsides of any two slabs are grouted to provide a rigid joint, every slabhaving hollow longitudinal passages extending the full length thereof,the area of the passages in a slab section constituting between about40% and about 50% of the total sectional area of the slab, every slabhaving straight longitudinal steel reinforcement members adjacent thebottom and top corners of the slab and extending straight for the fulllength of the slab and steel stirrup means for the suspended slabs onlyrigidly secured to the bottom corner reinforcing members and extendingupwardly toward the top face of the slab, each steel stirrup meanshaving support portions just clearing the top slab face and extendinglongitudinally beyond the end of the suspended slab and overlying thetop of the adjacent end of a supporting slab, said entire constructionusing steel reinforcement so efficiently that, with the same amount ofsteel reinforcement in an entire construction, slab deflection betweenrigid support regions is reduced by about 30% compared to a simple spanconstruction having similarly spaced rigid supporting regions wherebysaid continuous slab construction can use less steel for the samedeflection or can reduce deflection with the same amount of steel ascompared to a simple span construction.

2. The construction according to claim 1 wherein all the steelreinforcement in the supporting slabs are prestressed and wherein thereinforcing members in the bottom only of the suspended slabs areprestressed.

3. The construction according to claim 1 wherein each slab has anadditional longitudinal steel reinforcement adjacent the bottom face butdisposed between longitudinal passages and wherein stirrup means arerigidly attached to all of the bottom longitudinal reinforcing members.

4. The construction according to claim 1 wherein an angle iron isrigidly attached to said stirrup means, said angle iron having one partextending across the end face of the suspended slab and having the otherpart extending away from the end face and overlying the top face at theend portion of the adjacent supporting slab.

References Cited in the file of this patent UNITED STATES PATENTS1,049,702 Grady Jan. 7, 1913 1,241,187 Berliat Sept. 25, 1917 1,579,015Marks Mar. 30, 1926 1,778,315 Ferguson Oct. 14, 1930 1,850,735 VenzieMar. 22, 1932 1,921,285 Davis et al. Aug. 8, 1933 2,103,969 Davis et al.Dec. 28, 1937 2,234,114 Gifford Mar. 4, 1941 2,299,070 Rogers et al.Oct. 20, 1942

